How do masters practice their art? By practicing perfect.
I learned this at an Arts conference 10 years ago.
2 speakers - the first played bass and the second played flute. Their point was to make every detail perfect when practicing. For example, don't practice speed when running scales. Practice making every note ring perfect - no fret buzzing, no accidental notes, everything in time with a metronome. Every. Single. Note. Perfect and in perfect time. Another ex - switching between a G chord and a B minor without being sloppy or buzzing - just switching back and forth for 10 minutes with zero flaws.
And the flute player? He said he plays single notes drawing them out, not letting them lose strength or momentum.
Masters slow down with extreme focus on specific areas that others might overlook.
If I were a smarter man, I'd be able to relate this post to comic books or illustration.